1. Field of Invention
The invention relates to a structure of a vehicular power transmission device. In particular, the invention relates to a support structure for a differential device provided in a vehicular power transmission device.
2. Description of Related Art
A differential limiting device using a planetary gear is known as a differential limiting device that is used in a center differential of a vehicle or the like to generate differential limiting force during the drive force distribution and the differential operation between the front and rear wheels. FIG. 4 is a sectional view of a differential limiting device 100 using a planetary gear according to a technology related to the invention. The meshing teeth of the pinion gears P, the ring gear R and the sun gear S of the planetary gear are helical teeth. The ring gear R and the sun gear S are coaxially disposed on an axis D so as to be rotatable relative to each other. The helical teeth of the pinion gears P are meshed with the helical teeth of the ring gear R and the sun gear S, and the carrier CA is disposed on the axis D coaxially with the sun gear S so as to be rotatable relative to the sun gear S and the ring gear R, and supports the pinion gears P freely rotatably. It is to be noted herein that the meshing of the helical teeth of the pinion gears P with the helical teeth of the ring gear R and of the sun gear S allows thrust force to be generated. When the pinion gears P rotate (rotate about their own axes) in a direction, the thrust forces generated on the sun gear S and the ring gear R press the ring gear R or the sun gear S against the carrier CA; thus, the differential motion is limited so as to lessen the rotation difference of the carrier CA with the sun gear S and the ring gear R.
In the differential limiting device 100 constructed as described above, it is necessary to provide a structure that supports the thrust forces that are generated on the sun gear S and the ring gear R, in other words, the structure that receives the thrust forces that are generated on the sun gear S and the ring gear R. Therefore, a housing 102 is provided so as to cover the ring gear R, and the thrust forces are supported by the housing 102 via a thrust washer 104 disposed between the ring gear R and the housing 102, and a thrust washer 106 disposed between the carrier CA and the housing 102. Hence, in the differential limiting device 100, since it is necessary to dispose the housing 102 for supporting the thrust force, there is a problem of the differential limiting device 100 increasing in size by an amount that corresponds to a thickness (Aa) of an outer wall of the housing 102.
Against this problem, Japanese Patent Application Publication No. 2005-337442 (JP-A-2005-337442) discloses a technology regarding a differential limiting device in which the carrier and the sun gear are sandwiched by a first side wall portion and a second side wall portion that extend radially inward from two end portions of the ring gear. Therefore, the technology is able to thoroughly perform a differential limiting function without the provision of a housing that covers the ring gear from outside.
In conjunction with a vehicular power transmission device equipped with a differential limiting device disclosed in Japanese Patent Application Publication No. 2005-337442 (JP-A-2005-337442), no teaching or mention is disclosed regarding the arrangement of bearings that support, in axial and radial directions, an input shaft connected to the differential limiting device and various other elements that constitute the differential limiting device. However, from viewpoints of reduction of vibration, further size reduction of the device, and supply of stabilized differential limiting torque, there is a need to set an appropriate arrangement of bearings and the like.